1. Field of the Invention
The present invention relates to the forming of a controlled rectifying bridge, or composite bridge.
2. Discussion of the Related Art
FIG. 1 shows the conventional diagram of a composite bridge intended for continuously supplying a load 1. This bridge is connected by terminals 2 and 3 to the A.C. power system, terminal 3 being considered as the reference terminal. The anode of a diode D1 and the cathode of a diode D2 are connected to terminal 2. The cathode of diode D1 and the anode of diode D2 are connected across load 1. A thyristor Th1 is connected by its anode to terminal 3 and by its cathode to the cathode of diode D1. A thyristor Th2 is connected by its cathode to terminal 3 and by its anode to the anode of diode D2. With such a bridge, a rectified current can be made to flow through load 1. Further, triggerings on halfwave portions can be implemented, which is currently called a phase-angle control.
The bridge of FIG. 1 has many advantages as compared to the various other known controlled bridge assemblies. As compared to a bridge including two thyristors in series, it has the advantage that diodes D1 and D2 are used as free wheel diodes during the phases when thyristors Th1 and Th2 are off. As compared to a bridge with 4 diodes in series with a triac, it especially has the advantage that, when on, the voltage drop is reduced substantially by the voltage drop of a forward diode.
Despite these advantages, the assembly of FIG. 1 is seldom used, because of a thyristor control problem. Indeed, thyristors Th1 and Th2 are controlled by gate voltages respectively referenced to their cathodes. Now, the cathodes of thyristors Th1 and Th2 are not at the same potential. This requires the use of relatively complex distinct control circuits, and frequently isolated control circuits, the isolation being ensured, for example, by a transformer or by optically controlled components. Further, in known circuits, both thyristors Th1 and Th2 are generally made in the form of discrete components.
U.S. Pat. No. 5,365,086, which is incorporated herein by reference, describes a thyristor, the cathode of which corresponds to the rear surface of the component coated with a single metallization connected to a reference terminal, and the control terminal of which is taken on the opposite side and is referenced to the cathode. It could be imagined to use this thyristor to replace thyristor Th2 of FIG. 1. However, this patent does not suggest how to associate a thyristor to a thyristor of opposite biasing.
U.S. Pat. No. 6,034,381, which is incorporated herein by reference, describes a bidirectional switch (ACS), the control electrode of which is arranged on the surface opposite to a common surface, the control voltage being referenced to this common terminal. However, this patent only describes a bidirectional switch with a single control terminal and two main electrodes only, and does not indicate how to form two thyristors having a common main terminal and the other terminals of which are distinct.
Thus, an object of the present invention is to provide a monolithic component corresponding to two thyristors connected by one of their main terminals of opposite biasing forming a surface of the component, a single control terminal enabling operation of the two thyristors being arranged on the opposite component surface at the same time as the other main terminal of each of the thyristors.
To achieve this and other objects, the present invention provides a monolithic component including two thyristors of a composite bridge connected to an A.C. voltage terminal by a common terminal corresponding to a common rear surface metallization forming an electrode of opposite biasing of each thyristor, including, in a substrate of a first conductivity type, an isolating wall separating the substrate in two portions, a first portion including on its lower surface side an anode region and on its upper surface side a cathode region, the second portion including on its lower surface side a cathode region and on its upper surface side an anode region, the isolating wall surrounding each of the components extending towards the main electrode on the side which carries no common metallization and including in this extended region an area of the second conductivity type, the two areas being connected together to a common control terminal.
According to an embodiment of the present invention, on the upper surface side, the cathode gate region in which the cathode region of a first thyristor is included, as well as the anode region of the other thyristor, is surrounded by a ring of a first conductivity type of high doping level formed in the substrate.
The foregoing objects, features and advantages of the present invention, will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings.